1. Field of the Invention
The present invention relates generally to caster assemblies for material handling carts, and more particularly to a caster assembly having a thread guard to help prevent strands of foreign material from wrapping around the caster axle.
2. Description of the Prior Art
A caster is a wheel or rotating ball mounted in a swivel frame that may be used for the support and movement of furniture, trucks, portable equipment, material handling carts, and the like. The swivel frame may be referred to as a “caster horn” or “yoke,” and the yoke may be said to have “yoke legs,” which extend toward the wheel on either side of the wheel. Because the caster wheel is frequently mounted with an offset in a swivel frame (i.e., a frame where a swivel axis is offset from an axle axis), the wheel usually rotates in one direction with the wheel trailing the swivel mounting.
When the caster is used in an environment that has strands of material on the floor, the caster wheel may pick up a strand and wrap it around the axle. Such strands of material may include hair, string, threads from clothing, mop strings, or the like. The strands may be picked up by the wheel because the strands are very light, or because the surface of the wheel may be tacky due to wetness or other sticky substances that may be on the wheel tread.
Although any wheel may accumulate strands around its axle, this problem is more severe when the caster wheel rotates primarily in one direction. A strand wrapped over or around the axle will tend to stay there as other strands accumulate on top, and the strands are pulled tighter as they are all wrapped in the same direction. These accumulated strands may interfere with the smooth operation of the bearing, and may trap dirt and other contaminants near the bearings, which may reduce the function or the life of the bearing. Strands collected around the axle are also unsightly and may leave a poor impression in a customer's mind, reflecting upon the quality and cleanliness of a retail store as the customer operates a dirty, wobbly, and hard-to-push shopping cart.
For these reasons, caster designers continue to pursue designs that discourage the wrapping of strands of material around the axle of a wheel.
In the prior art, many manufactures offer devices called “thread guards.” For example, a thread guard is disclosed in U.S. Pat. No. 5,518,322 granted to Hicks on May 21, 1996, which is incorporated herein by reference. The Hicks thread guard is circular, with an opening for the axle bolt in the center. The thread guard does not rotate with the wheel; it is stationary with respect to the caster yoke. The thread guard extends radially from the plane of the axle opening and then curves toward the medial plane of the wheel hub, extending to points inside the concave recess in the hub (i.e., inside the plane of the outer hub face).
Other designs may use the shape and configuration of the yoke legs as a thread guard.
There continues to be a need for an improved thread guard and caster assembly that either prevents or reduces the likelihood that strands picked up by the wheel will become wrapped around the axle. Such a thread guard will improve the performance and reliability of wheels used on material handling carts, and will help maintain the aesthetically pleasing appearance and operation of a new caster.